Soft, thick, non-linting nonwoven

ABSTRACT

The nonwoven web  10  of the present invention is a layered structure that takes advantage of the beneficial properties of different types of fibers advantageously distributed in each layer. In particular, the present invention is a multi-layer nonwoven web suitable for use as a wet wipe, the web having a first fibrous outer layer comprising from about 10% to about 60% conjugate fiber, from about 10% to about 90% cellulosic fibers, a fibrous inner layer bonded at discrete bond sites to the first outer layer in a face to face relationship comprising from about 10% to about 60% conjugate fiber, and from about 10% to about 65% cellulosic fibers. A second fibrous outer layer, which can be the same composition as the first outer layer, is bonded at discrete bond sites to the inner layer in a face to face relationship. A method for forming the web of the present invention is also disclosed.

CROSS REFERENCE TO RELATED APPLICATION

This patent application is a continuation of Nonprovisional Utilitypatent application Ser. No. 09/824,454, filed Apr. 2, 2001, which claimspriority to Provisional Patent Application Ser. No. 60/196,972, filedApr. 13, 2000, the substances of which are incorporated herein byreference.

FIELD OF THE INVENTION

The present invention is related to nonwoven materials. In particular,the present invention is related to soft, thick, and non-lintingnonwoven materials suitable for use as a substrate for pre-moistenedwipes.

BACKGROUND OF THE INVENTION

Nonwoven fabrics are desirable for use in a variety of products such asbandaging materials, garments, disposable diapers, and other personalhygiene products, including pre-moistened wipes. Pre-moistened wipes areoften packaged as discrete wipes in a stack in a moisture proofcontainer, and are often referred to as wet wipes. Wet wipes arecommonly used as baby wipes for the cleaning of a baby's skin during adiaper change.

Nonwoven fabrics having high levels of strength, thickness, drape, andsoftness are desirable for body-contacting articles, such as linings fordisposable diapers and wet wipes. However, optimizing all the desirableproperties is often not possible. For example, often a balance ofproperties results in less than desirable softness or strength levels.Wet wipes used as baby wipes, for example, should be strong enough whenwet to maintain integrity in use, but soft enough to give a pleasing andcomfortable tactile sensation to the user(s). In addition they shouldhave fluid retention properties such that they remain wet duringstorage, and sufficient thickness and porosity to be effective incleaning the soiled skin of a user.

Strength in a nonwoven fabric can be generated by a variety of knownmethods. If thermoplastic fibers are used, strength can be imparted bymelting, either by through-air bonding or by hot roll calendaring.Hydroentangling fibers in a spunlace operation and adhesive bonding arealso commonly used to bind fibers to increase the strength of thenonwoven. However, these processes, while increasing the strength of thenonwoven, generally detract from other desirable properties. Forexample, thermal bonding is effective at maintaining the thickness(bulk) of the nonwoven, but maintaining a relatively soft productsuitable for wet wipes requires the use of relatively expensiveconjugate fibers throughout the nonwoven web. The use of conjugatefibers throughout the nonwoven can also negatively affect the drape ofthe resulting material.

Hydroentangling a fibrous structure generates strength, but typicallyreduces the thickness of the material. Such a reduction in thickness isundesirable in a wet wipe application. Due to the nature of cleaningtasks for which wet wipes are used, consumers prefer a wipe that has aminimum amount of apparent bulk, or thickness associated with it. Toincrease the basis weight of the starting material such that afterhydroentangling the material retains sufficient thickness to be used asa baby wipe would be prohibitively expensive.

Adhesive bonding can be used to generate sufficient strength, especiallyin a carded web. However, adhesive adds to the expense of the resultingweb, often costing more than the fibers of the base web to which it isapplied. Additionally, the presence of adhesive can negatively impactthe fragrance and preservative ingredients in a wet wipe. Adhesiveapplication systems also add cost and complexity to a nonwovenmanufacturing process, as well as creating hygiene problems in theapplication equipment and other equipment in the vicinity. Finally,adhesive can contribute to the stiffness of the final nonwoven, whichlowers the drape and perceived softness of the material.

In addition to the attributes of relatively high strength, drape, andsoftness, another property desirable in a nonwoven suitable for a wetwipe is relatively low linting. Linting, or pilling, occurs as fibers,or small bundles of fibers, are pulled off, or otherwise released from,the surface of the nonwoven substrate of the wet wipe. Linting resultsin fibers remaining on the skin of the user, a highly undesirablecondition for wet wipe users. Linting can be controlled in much the sameway that strength is imparted. That is, to the extent that fibers of thenonwoven are bonded to, or entangled with, one another, Tinting levelscan be controlled. Therefore, by increasing the level of adhesive in acarded web, for example, Tinting can be decreased. However, as mentionedabove, the increased level of adhesive contributes to greater stiffnessand decreased levels of softness.

Accordingly, it would be desirable to have a soft, thick nonwoven websuitable for use as a wet wipe, and having suitable strength to maintainstructural integrity during use.

Additionally, it would be desirable to have a soft, thick nonwoven websuitable for use as a wet wipe for effective skin soil cleaning.

Additionally, it would be desirable to have a thick and soft nonwovenweb suitable for use as a wet wipe exhibiting relatively low levels ofTinting without the use of stiffness-increasing additives, such as theaddition of adhesive.

Additionally, it would be desirable to have a nonwoven web suitable fora wet wipe that exhibits relatively high retention of fluids such asaqueous fluids, and relatively high strength, but remains soft to theskin, with sufficient thickness, texture and porosity for effective skinsoil cleaning.

Finally, it would be desirable to have a nonwoven web, suitable for awet wipe that can be made with a relatively high strength, thickness andsoftness, without linting, and can be made economically.

SUMMARY OF THE INVENTION

The nonwoven web 10 of the present invention is a layered structure thattakes advantage of the beneficial properties of different types offibers advantageously distributed in each layer. In particular, thepresent invention is a multi-layer nonwoven web suitable for use as awet wipe, the web having a first fibrous outer layer comprising fromabout 10% to about 60% conjugate fiber, from about 20% to about 65%cellulosic fibers, a fibrous inner layer bonded at discrete bond sitesto the first outer layer in a face to face relationship comprising fromabout 10% to about 60% conjugate fiber, and from about 10% to about 90%cellulosic fibers. A second fibrous outer layer, which can be the samecomposition as the first outer layer, is bonded at discrete bond sitesto the inner layer in a face to face relationship. In a currentlypreferred embodiment each layer also has a certain percentage ofmulti-component, or conjugate fiber, such as bicomponent fiber.

A method for forming the web of the present invention is also disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified perspective view of one embodiment of a nonwovenweb of the present invention utilized as a wet wipe, showing only aportion of the embossed area.

FIG. 2 is a schematic representation of an apparatus for producing anonwoven web of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The nonwoven web 10 of the present invention is a layered structure thattakes advantage of the beneficial properties of different types offibers advantageously distributed in each layer. In particular, in acurrently preferred embodiment, as shown in FIG. 1, the nonwoven web ofthe present invention is at least a three-layer structure having atleast one relatively high basis weight central layer 12 disposed betweentwo relatively low basis weight outer layers, 14 and 16. By “layer” asused herein is meant a portion of a web that is formed as a discrete webapart from other layers, for example by its own card in a cardingoperation, prior to being joined to adjacent layers to form a unitaryweb. A layer is made as a relatively homogeneous web, that is, theconstituent fibers are relatively evenly distributed within the layer.Unless otherwise noted all percentages given herein are weightpercentages.

When formed by the method of the present invention, the nonwoven web 10exhibits a good balance of strength, extensibility, thickness, drape,and softness, which are desirable for body-contacting articles, such aslinings for disposable diapers and wet wipes. The web 10 also exhibitsvery low levels of linting, and controlled stretch properties, whichmakes it particularly useful as a substrate for pre-moistened wipes,otherwise known as wet wipes. However, it is recognized that thenonwoven web 10 can have other useful and beneficial uses as well.Therefore, a wet wipe is taught herein as a preferred, but non-limitinguse for the nonwoven web 10.

In a currently preferred embodiment, the constituent outer layers of thenonwoven web 10 are formed by carding. Carding is a mechanical processwhereby clumps of staple fibers are separated into individual fibers andsimultaneously made into a coherent web. Carding is typically carriedout on a machine that utilizes opposed moving beds or surfaces of fine,angled, closely spaced teeth or wires or their equivalent to pull andtease the clumps apart. The teeth of the two opposing surfaces typicallyare inclined in opposite directions and move at different speedsrelative to each other.

In a currently preferred embodiment, the constituent inner layer of thenonwoven web 10 is formed by an air laying process. Air laying is aprocess whereby air is used to separate, move, and randomly depositfibers from a forming head to form a coherent, and largely isotropicweb. Air laying equipment and processes are known in the art, andinclude Kroyer or Dan Web devices (suitable for wood pulp air laying,for example) and Rando webber devices (suitable for staple fiber airlaying, for example).

The nonwoven web 10 of the present invention and a method of making arenow described below with reference to FIGS. 1 and 2, respectively.

The Nonwoven Web

In a currently preferred embodiment, the two outer layers 14 and 16 ofnonwoven web 10 are identical, and each will be so described in detailherein with reference to outer layer 14. However, it is recognized thatthe two outer layers need not have identical compositions, basisweights, or other material properties.

The invention is described below as a three-layer web having a singleinner layer with two outer layers. However, it is recognized that therecan be more than one inner layer. For example, instead of one airlaidforming head making the inner layer, two or more heads can make up twoor more inner layers. However, the percentages for the variousproperties of the inner layer below can apply to the inner layers as awhole, if more than one inner layer is used between the outer layers.

In the currently preferred embodiment described herein, the nonwoven web10 is formed without the use of adhesive. That is, the web is formed bya method that does not involve the application of adhesive, andtherefore the finished layered unitary web is characterized by theabsence of adhesive or an adhesive component. Although in less preferredembodiments an adhesive can be used, in a currently preferred embodimentthe layers are held together to form a unitary web only by fiber tofiber thermal bonds. FIG. 1 shows a portion of an embossed area 18 whichcan be a thermal bond location.

In each layer of the nonwoven web 10 of the present invention acombination of fiber types is utilized to optimize the beneficialproperties of each. For example, the outer layers can have a certainpercentage of cellulosic fibers to give the web a soft, cloth-like feel;while the inner layer may have a different percentage of the same orsimilar cellulosic fibers to provide for improved absorbency andthickness. Each layer also has a certain percentage of multi-component,or conjugate fiber, such as bicomponent fiber, to provide for thermalbonding and softness Other fibers, for instance polypropylene,polyester, polypropylene-polyester conjugates and polyester-polyesterconjugates fibers may be added in each layer to achieve additionalproperties such as thickness, softness and drape. In a currentlypreferred embodiment, the nonwoven web 10 of the present inventioncomprises the above-mentioned cellulosic and conjugate fibers inpre-determined proportions, as described more fully below.

The outer layers 14 and 16 can each make up from about 10% to about 40%of the total basis weight of nonwoven web 10. In one preferredembodiment, each outer layer about 10% to about 30% of the total basisweight of nonwoven web 10, and in a currently preferred embodiment thetwo outer layers 14 and 16 are identical and each comprise about 18% ofthe total basis weight of the nonwoven web 10.

The inner layer 12 can make up from about 33% to about 80% of the totalbasis weight of nonwoven web 10. In a currently preferred embodiment,the inner layer 12 comprises about 62% of the total basis weight of thenonwoven web 10.

The outer layers 14 and 16 should have sufficient quantity of conjugatefibers to permit adequate fiber-to-fiber bonding within the layers, andfiber-to-fiber bonding with fibers in the central layer 12. Adequatefiber-to-fiber bonding is achieved when loose surface fibers are “tieddown” such that they are not easily dislodged from the nonwoven web inthe form of lint. Therefore, each outer layer can have from about 10% toabout 60% conjugate fibers. In one preferred embodiment, each outerlayer has about 25% to about 60% conjugate fibers. Without being boundby theory, is believed that 25% of conjugate fibers is the minimumamount necessary to adequately tie down loose surface fibers forconsumer-acceptable low-linting wet wipe applications. In a currentlypreferred embodiment the two outer layers 14 and 16 each comprise about50% conjugate fibers.

The inner layer 12 should also have sufficient quantity of conjugatefibers to permit adequate fiber-to-fiber bonding, particularly bondingwith the fibers of the outer layers. Although a structure of separatelayers permits preferential distribution of fiber types, it remainsimportant that the constituent layers perform as a unitary web whenutilized as a wet wipe, particularly in a baby wipe application.Delamination of the layers during use detracts from the consumerbenefits delivered from such a wet wipe. Therefore, to avoiddelamination of the layers, the inner layer can have from about 10% toabout 60% conjugate fibers. In one preferred embodiment, the inner layerhas about 15% to about 50% conjugate fibers, and in a currentlypreferred embodiment the inner layer 12 comprises about 20% conjugatefibers which, without being bound by theory, is believed to be theminimum amount necessary to maintain structural integrity and to preventdelamination in consumer-acceptable wet wipe applications.

The outer layers 14 and 16 should have sufficient quantity of cellulosicfibers to give the nonwoven web 10 a soft, clothlike feel. Each outerlayer can have from about 30% to about 65% cellulosic fibers. In oneembodiment each outer layer has about 25% to about 70% cellulosicfibers. Without being bound by theory, is believed that 25% cellulosicfibers is the minimum amount that can be used and still deliver apreferred clothlike feel in consumer-acceptable wet wipe applications.In a currently preferred embodiment the two outer layers 14 and 16 eachcomprise about 50% cellulosic fibers.

The inner layer 12 can have a quantity of cellulosic fibers sufficientto give the nonwoven web 10 adequate absorbency. Especially when used asa wet wipe, each wipe should exhibit sufficient absorbency to absorb andhold aqueous fluids or lotions prior to use. Additionally, fluid, suchas urine, should be sufficiently absorbed so as to make the wipe iseffective in cleaning tasks associated with baby wipes. The inner layercan have from about 10% to about 100% cellulosic fibers. The inner layercan have about 25% to about 90% cellulosic fibers, and in a currentlypreferred embodiment the inner layer 12 comprises about 80% cellulosicfibers. In particular, using 80% cellulosic content in the inner layer12 together with the preferred percentages shown above for the outerlayers, gives a total substrate content of about 68% cellulose, whichhas been found to be beneficial in baby wipe applications. Without beingbound by theory, about 40% cellulosic fiber content is believed to bethe minimum amount necessary for adequate absorbency inconsumer-acceptable wet wipe applications. In one embodiment, thecellulosic content can be a combination of low denier rayon fibers andfluff pulp fibers. A preferred pulp fiber is Foley Fluff available fromBuckeye Technologies, Memphis, Tenn.

For each of the layers, the conjugate fibers can be of a core/sheathdesign, and are preferably comprised of polypropylene (as the core) andpolyethylene (as the sheath). In a preferred embodiment for the outerlayers, the conjugate fibers can be from about 20 mm to about 60 mm inlength, and in a preferred embodiment are about 40 mm in length. Apreferred conjugate fiber is a 1.7 dtex, 40 mm fiber available as ES-CPHIL from ES-FiberVisions, Covington, Ga. In a preferred embodiment forthe inner layers, the conjugate fibers can be from about 3 mm to about12 mm in length, and in a preferred embodiment are about 6 mm in length.A preferred conjugate fiber is a 1.7 dtex, 6 mm fiber available asAL-Adhesion C from ES-FiberVisions, Covington, Ga.

For the outer layers the cellulosic fibers can be rayon, and in apreferred embodiment are fibers low denier rayon fibers having a lengthof between about 20 mm and about 60 mm in length. In a preferredembodiment, the rayon is 1.5 denier fiber having an average length ofabout 40 mm. A preferred rayon fiber is available as type 18453,available from Acordis Cellulosic Fibers, Axis, Ala.

Method for Making

FIG. 2 shows a schematic representation of an apparatus for use in apreferred method of making the nonwoven web 10 of the present invention.As shown in FIG. 2, the method is a combination a of carding andairlaying processes, with subsequent through-air bonding and calendaringof the multi-layer substrate. Without being bound by theory, it isbelieved that the sequence of steps in the method described herein withreference to FIG. 2 is important to achieving the beneficial webproperties, as described below.

An apparatus, generally designated at 20, comprises a carding apparatushaving at least two cards designated at 22 and 26 and one airlay forminghead 24. Each component forms a discrete web. Any of these discrete webscould also be supplied as pre-bonded nonwoven roll goods. The first card22 forms a carded web corresponding to layer 16 as depicted in FIG. 1.Subsequently, the airlay forming head forms a web, layer 12, on top oflayer 16. Finally, card 26 forms a carded web, layer 14, which istransferred on top of layer 12.

Each carded web can be formed by carding methods known in the art, anddeposited by known methods, such as by doffing, onto a forming belt orscreen 28. Each airlaid web can be formed by airlaying methods known inthe art, and deposited by known methods onto a forming belt or screen28. As all three layers are formed on forming screen 28, forming screen28 is moved in the machine direction MD by rolls 29. In this way,nonwoven web 10 can be formed in a continuous process. The direction offorming is referred to as the machine direction MD, while the width ofthe web is measured in the cross direction CD.

The fiber composition of the fiber supply for each card and airlaidforming head can be predetermined, formulated and/or adjusted by methodsknown in the art for supplying mixed fiber cards and airlaying heads. Ina preferred process, and to produce a web having properties optimallysuited for use as a wet wipe, the fiber compositions can be prepared asfollows. For both cards 22 and 26, the preferred fiber composition is50% Type 18453 rayon and 50% ES-C PHIL PP/PE conjugate fiber, each ofwhich are described above. For the airlay forming head 24, the preferredfiber composition is 80% Foley Fluff and 20% AL Adhesion C conjugatefiber, each of which are described above.

After all three layers of the carded nonwoven web are deposited in alayered relationship, the deposited fibers are moved by forming screen28 to a thermal treatment apparatus 30. Thermal treatment apparatus 30can incorporate any of known methods for subjecting the layered web tosufficiently elevated temperatures so as to effect thermoplastic meltingof the polyethylene component of the constituent conjugate fibers. Uponcooling, portions of the conjugate fibers remain melt-bonded to portionsof adjacent conjugate fibers, thereby forming the three layers into aunitary web having substantially uniform distribution of layer to layerbond sites.

Fiber to fiber thermal bonds are preferably made by a through-air dryercomprising a through-air drying drum 32 which the carded web istransferred onto for a predetermined dwell time. The advantage of usinga through-air dryer is that the web is heated sufficiently with littleor no compression. In this manner, the constituent layers of the web canbe bonded together due to the conjugate fiber-to-conjugate fiberbonding, without unnecessary compression of calendaring rollers, forexample. Without wishing to be bound by theory, it is believed that thethrough-air bonding step tends to “set” the loft of the nonwoven byeffecting bonding without unnecessary compression. This “loft setting”produces a bulkier sheet for better thickness in the end product. Byusing the composition percentages described above, the thickness of thefinished product is believed preferred by consumers using the web as awet wipe.

The through-air thermal bonding process can be carried out by methodsknown in the art for through-air drying webs, including paper webs. Ingeneral, the nonwoven web is guided and removed from screen 28 andplaced in contact with a rotating perforated drying drum 32. Hot air ofsufficient temperature is forced out of the perforated drying drum 32and through the nonwoven web being thermally treated. The airtemperature, air volume, and machine direction line speed of productioncan be adjusted to ensure sufficient dwell time for adequatefiber-to-fiber bonding. The actual time, temperature, and line speed canbe varied as appropriate, and is not considered to be critical.

After being thermally bonded, the layered, bonded web is then continuesfor further processing to a calendaring apparatus 40. Calendaringapparatus 40 preferably comprises thermal embossing means to impart anembossed pattern of compressed regions onto the layered, bonded web. Theembossing means can include standard embossing patterns and equipment asare known in the art.

By embossing the layered, bonded nonwoven web, the nonwoven web can gainbetter aesthetics, particularly for use as a wet wipe. However, besidesbetter aesthetics, other beneficial physical characteristics areimparted to the nonwoven web by calendaring. For example, by calendaringthe web at sufficiently elevated temperatures additional thermal bondingis achieved in the compressed regions, thereby giving better surfacefiber bonding. This surface fiber bonding “ties down” loose fiber,resulting in reduced Tinting of the finished web. Additionally thethermal bonding of the calendaring operation increases the strength ofthe nonwoven web 10, especially when used in a wet wipe application. Theadded embossing also produces a web having a topography that exhibitssufficient texture and porosity for effective skin soil cleaningFinally, the thermal emboss contributes to reducing the availablecross-direction CD stretch of the finished web. Excessive CD stretch isoften a characteristic of carded webs, and is generally undesirable in awet wipe. By reducing CD stretch, the stretch properties of the web aremore uniform, and more suited for use as a wet wipe.

The thermal embossing can be carried out by suitable methods known inthe art. In one embodiment satisfactory results were produced by settingthe calendaring apparatus 40 temperatures at 145 degrees Centigrade onthe pattern roll 42, and on the anvil roll 44. A nip pressure of about264 pound per linear inch produces satisfactory results for thepreferred web described above, having three layers and a total basisweight of 64 grams per square meter (gsm).

The layered, bonded, and calendared web can then be wound as roll stockon a parent roll 50 for storage or further processing.

While particular embodiments and/or individual features of the presentinvention have been illustrated and described, it would be obvious tothose skilled in the art that various other changes and modificationscan be made without departing from the spirit and scope of theinvention. Further, it should be apparent that all combinations of suchembodiments and features are possible and can result in preferredexecutions of the invention. Therefore, the appended claims are intendedto cover all such changes and modifications that are within the scope ofthis invention.

1. A multi-layer nonwoven web suitable for use as a wet wipe, the webcomprising: (a) a first fibrous outer layer comprising from about 10% toabout 60% conjugate fiber, from about 20% to about 65% cellulosicfibers; (b) a fibrous inner layer comprising from about 10% to about 60%conjugate fiber, from about 10% to about 90% cellulosic fibers, theinner layer bonded at discrete bond sites to the first outer layer in aface to face relationship; and (c) a second fibrous outer layercomprising from about 10% to about 60% conjugate fiber, from about 20%to about 65% cellulosic fibers, the second fibrous outer layer bonded atdiscrete bond sites to the inner layer in a face to face relationship.2. The nonwoven web of claim 1, wherein the first and second outer layercomprise identical fiber compositions.
 3. The nonwoven web of claim 1,wherein the first and second outer layers together comprise from about20% to about 80% of the total basis weight of the web.
 4. The nonwovenweb of claim 1, wherein the first and second outer layers each comprisefrom 20% to about 60% of the total basis weight of the web.
 5. Thenonwoven web of claim 1, wherein the inner layer comprises from about33% to about 80% of the total basis weight of the web.
 6. The nonwovenweb of claim 1, wherein the web is formed in the absence of adhesive. 7.The nonwoven web of claim 1, wherein the first and second fibrous layersare carded.